The efficiency of the fuel combustion determines the main operational characteristics of the engine: overall efficiency, noise, emissions, etc. Typical fuel supply systems and systems for injecting and dispersing fuel in the combustion chamber have their own limitations.
Usually to improve gas turbine engine performance a two-stage combustion changing system is suggested. In such type of engine a diffuse combustion mode is used to start the engine or operate it at decreased loads. When gas turbine engine operate at normal loads or continuous working loads a premix fuel/air combustion mode is used that improve emission efficiency.
There are known approaches where to reduce fuel consumption an incombustible liquid, water, is added. At high temperature in the combustion chamber water evaporates and resulted superheated steam significantly increases the pressure in the combustion chamber. Thereby rises the enthalpy of the combustion process as well as overall engine efficiency. In practice such approaches were used with short-lived engines such as engines for military applications. Experiments with gas-turbine engines used for natural gas pumping showed fuel efficiency of up to 25%, but adverse effect on service life. The life of the gas-turbine engine operating at constant loads reduced significantly (in more than 10 times) due to corrosion of working parts as during vaporization there are some liquid water droplets that do not evaporate fast enough. Special treatments of the water to reduce its corrosion activity did not give acceptable results. In case of gas-turbine engines operating at variable loads such as engines for marine and aviation applications the problem of corrosion becomes more aggravated and does not allow using that approach.
In general the technology of utilizing the combustion heat by addition of evaporative liquid is under development by some companies. For example, BMW has announced about development of a special additional turbine to be installed downstream the main turbine and injection of water in the exhaust stream in the inlet of the additional turbine. Similar approaches are under development in some US companies in order to increase the engine efficiency and reduce fuel cost.